Closed captioning provides a visible text representation of a television program's audio content. Closed captioning data is encoded in an auxiliary information signal of the video signal. For example, in NTSC (National Television Standards Committee) television signals, two bytes of closed captioning data may be included during the latter half of each occurrence of line 21 of field 1. Additional closed caption data and similarly encoded information, such as extended data services information (XDS), may be included in other line intervals such as line 21 of field 2. United States law requires caption decoders in all television receivers having cathode ray tubes (CRT) larger than 13 inches. Therefore, most programs (video tapes included) now include captioning data.
Although captioning was developed to aid the hearing impaired, captioning can also provide a benefit to non-hearing impaired viewers as well. Providing captioning representing the audio program associated with an auxiliary image in a multi-image display, such as picture-in-picture (PIP) or picture-outside-picture (POP) displays, is an example of this type of additional benefit. As a specific example, activating a PIP feature produces a small image representing the content of a PIP program signal to be displayed in a portion of the main picture. However, only the audio program associated with the main picture is processed and coupled to the speakers of the television. The audio content of the PIP signal is lost. Because the audio program is important to the comprehension of a television program, the usefulness of the PIP feature is severely limited by the lack of an associated audio program. An approach to solving this problem is to display captions, i.e., visible text, representing the PIP audio programming portion of the display. However, the closed caption decoder in most television receivers processes only the caption information associated with the main picture, not the PIP signal.
An exception to this general rule is found in certain television receivers manufactured by Sharp Corporation such as model 31HX-1200 and 35HX-1200. These Sharp television receivers display captions representing the audio PIP image by providing switching capability that permits coupling of the PIP signal to the main caption decoder. PIP captions are displayed full size (up to 4 rows of 32 large characters) at the top or bottom of the screen (a user selectable position). An example of PIP captioning used by Sharp television receivers is shown in FIG. 1 which depicts a display including main image 100, PIP image 102 and PIP caption 104.